Heavy oil is a term commonly applied to describe oils having a specific gravity less than about 20° API. These oils, which include oil sand bitumen, are not readily producible by conventional techniques. Their viscosity is so high that the oil cannot easily be mobilized and driven to a production well by a pressure drive. Therefore, a recovery process is required to reduce the viscosity and then produce the oil.
Thermal recovery methods as applied in heavy oil have the common objective of accelerating the recovery process. Raising the temperature of the host formation reduces the heavy oil viscosity, allowing the near solid material at original temperature to flow as a liquid. It is known in the art of hydrocarbon recovery, and particularly in the recovery of heavy and unconventional hydrocarbons from subsurface reservoirs, to employ the use of steam or steam-solvent mixtures as injectants to reduce the viscosity of the hydrocarbons and allow them to flow to a producing well and thereby be produced to surface. For example, cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) methods employ steam to mobilize subsurface heavy hydrocarbon such as heavy oil or bitumen. However, the effectiveness of steam injection methods is limited in most cases to about a 2500 ft. depth. At such depth, heat losses in surface steam lines and in the wellbore reduce the steam quality to a value generally insufficient to provide the high heat ratio at the reservoir required for an economical oil flow rate. These oils are often produced as emulsions with water by using common recovery techniques.
There are certain other situations where steam injection may not work well. These situations can include the following:                Thin pay-zones, where heat losses to adjacent (non-oil-bearing) formations may be significant.        Low permeability formations, where the injected fluid may have difficulty penetrating deep into the reservoir.        Reservoir heterogeneity, where high permeability streaks or fractures may cause early injected fluid breakthrough and reduce the sweep.        
It has long been recognized that such recovery methods can be costly to implement and operate and requires access to significant water resources. Alternative methods have accordingly been developed that employ electromagnetic heating techniques, in which antennae are positioned downhole adjacent a target reservoir and generate electromagnetic energy to heat and thereby mobilize the heavy hydrocarbons, enabling production to surface.
Electromagnetic (EM) heating has been considered as a viable alternative to steam-based thermal processes since electrical instruments are widely available and its use requires a minimal surface presence, so it is particularly favorable in populated areas or in offshore sites. EM heating is a thermal process, which may be applied to a well to increase its productivity by the removal of thermal adaptable skin effects and the reduction of oil viscosity near the well bore. Electric current leaves the power supply and is conducted down by the power delivery system (transmission line) to the antenna assembly for the radio frequency (RF) case. The antenna is an electrical device that can radiate the EM energy into the reservoir formation.
EM-thermal processes are generally understood to be free of issues related to very low initial formation injectivity, poor heat transfer, shale layers between rich oil layers, cap rock requirement, and the difficulty of controlling the movement of injected fluids and gases, all of which have impacted other thermal recovery processes such as SAGD. Apart from these, EM-thermal recovery is also commonly understood to present the following advantages when compared with other recovery technologies:                Heat is generated in-situ.        It does not need a working fluid.        It does not need a significant water supply.        It can reduce the produced water cut.        It is independent of formation permeability.        There is no apparent depth limit.        There is no emission concern.        There are no hazardous chemical concerns.        It increases apparent permeability.        It appears to be cost competitive to steam flood for shallow reservoirs and less expensive for deep reservoirs.        It heats uniformly and near-instantaneously from within and therefore is independent of the low thermal conductivity of the formation.        It increases the pressure and energy of the formation prior to production        
While it is commonly held that electromagnetic heating techniques may show promise in certain applications, it is believed that improvements and enhancements may be possible and render such methods even more desirable. In particular, issues arise with the use of antennas, and optimization may be possible.